The present invention relates to cesium salts and other alkali metal salts and methods of making the same.
Cesium salts, such as cesium formate, are increasingly being discovered as useful additives for a variety of industrial applications such as in the hydrocarbon recovery areas. Accordingly, there is a desire to develop processes which produce relatively high purity cesium salts efficiently and economically.
Previously, barium hydroxide and soluble barium salts have been used as reactants with cesium sulfate solutions in the formation of cesium salts. However, barium compounds are very expensive reactants and therefore undesirable.
Other processes have attempted to avoid the use of barium compounds and use cesium-aluminum-alum which is reacted in the presence of water with calcium hydroxide and a water soluble calcium salt. However, such a process requires the use of a soluble acid salt of lime, like calcium formate, and doesn""t address the removal of many impurities that exist in the cesium salt solution that is formed. There is also the very real risk of having soluble calcium salt contamination in the resultant product if the exact stoichiometric amount required is only slightly exceeded.
Accordingly, there is a need to develop improved processes for making cesium salts and other alkali metal salts which avoid one or more of the above-described disadvantages.
A feature of the present invention is to provide a method of making cesium salt and other alkali metal salts which avoids the exclusive use of expensive barium compounds.
Another feature of the present invention is to provide a method of making cesium salt which uses cesium sulfate as one of the starting reactants.
An additional feature of the present invention is to provide a process which forms relatively high purity cesium salts without large amounts of impurities.
Additional features and advantages of the present invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention will be realized and attained by means of the elements and combinations particularly pointed out in the description and appended claims.
To achieve these and other advantages, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention relates to a methods of making a cesium salt. In the methods, a cesium sulfate containing solution is reacted with lime to form a solution containing at least cesium hydroxide; and also formed is a residue containing calcium sulfate. The residue is then removed from the solution. The cesium hydroxide in the solution is then converted to at least one cesium salt. These steps can be repeated one or more times with the solution resulting in the last step in order to convert any remaining cesium sulfate, if desired, that remains in the solution.
The present invention further relates to a method of making cesium formate. In this method, a cesium sulfate containing solution is reacted with lime to form a solution containing cesium hydroxide and a residue containing calcium sulfate is also formed. The residue is removed from the solution. Afterwards, the cesium hydroxide in the solution is converted to cesium formate by the introduction of formic acid.
Furthermore, the present invention relates to a method of making cesium hydroxide which involves reacting a cesium sulfate containing solution with lime to form a solution containing at least cesium hydroxide and a residue containing calcium sulfate is also formed. The residue is then removed from the solution containing the cesium hydroxide.
Also, the present invention relates to a method of making an alkali metal salt comprising: a) reacting an alkali metal sulfate containing solution with lime to form 1) a solution comprising at least alkali metal hydroxide and 2) a residue comprising calcium sulfate; b) removing the residue from the solution; and c) converting the alkali metal sulfate hydroxide in the solution to at least one type of alkali metal salt.
In addition, the present invention relates to a method of making alkali metal hydroxide comprising: a) reacting an alkali metal sulfate containing solution with lime to form 1) a solution comprising at least alkali metal hydroxide and 2) a residue comprising calcium sulfate; and b) removing the residue from the solution.
The present invention also relates to a method of purifying alkali metal sulfate comprising: a) reacting an alkali metal sulfate containing solution with lime to form 1) a solution comprising at least alkali metal hydroxide and 2) a residue comprising calcium sulfate; b) removing the residue from the solution; and c) converting the alkali metal hydroxide in the solution to alkali metal sulfate, wherein the alkali metal sulfate in step c) has a purity higher than the alkali metal sulfate in step a).
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide a further explanation of the present invention, as claimed.
The present invention relates to a method of making a cesium salt and further relates to a method of making cesium hydroxide. The present invention, in addition, relates to methods of making alkali metal salts and alkali metal hydroxides.
In the preferred method of making cesium salts, a cesium sulfate containing solution is reacted with lime to form a solution comprising at least cesium hydroxide. A residue comprising calcium sulfate is also formed in the reaction, which is typically in the form of a precipitate. The residue comprising calcium sulfate is then removed from the solution and the cesium hydroxide in the solution is converted to at least one cesium salt.
The reacting of the cesium sulfate containing solution with the lime can occur at essentially any temperature and preferably occurs at a temperature of from about 0xc2x0 C. to about 100xc2x0 C., and more preferably occurs at a temperature of from about 0xc2x0 C. to about 50xc2x0 C., and even more preferably occurs at a temperature of from about 0xc2x0 C. to about 30xc2x0 C. Lower reaction temperatures are preferred in the present invention since the solubility of lime is significantly higher at lower temperatures. For instance, the lime solubility in the cesium sulfate containing solution is twice as high at about 20xc2x0 C. to about 25xc2x0 C. as compared to the lime solubility at 95xc2x0 C.
The cesium sulfate containing solution or slurry is typically an aqueous solution which contains any soluble amount of cesium sulfate in solution. For purposes of the present invention, suspended solids can be present in the solution. For instance, from about 0 ppm to about 3000 ppm of suspended solids can be present in the solution. Preferably, the suspended solids are not potentially soluble calcium salts. Thus, for purposes of the present invention, the cesium sulfate containing solution can also be considered a slurry. Preferably, from about 1% to about 50% by weight of cesium sulfate is present in the cesium sulfate containing solution, and more preferably from about 1% to about 10% by weight, and even more preferably about 5% by weight cesium sulfate in the cesium sulfate containing solution. The cesium sulfate can be obtained from a variety of sources including, but not limited to, filtration of neutralized cesium alum derived from pollucite ore digestions, filtration of neutralized cesium alums intentionally formed when recycling various cesium salt scraps, reprocessing to cesium sulfate salt from spent catalysts, and the like. Extremely pure or impure cesium sulfate solutions can be converted to the desired cesium salt.
The lime used to react with the cesium sulfate containing solution can be any type of lime and is preferably a calcium oxide or is a calcium hydroxide (also known as a hydrated lime). If calcium oxide is used, typically this lime forms a calcium hydroxide upon being combined with water or when introduced into the solution containing the cesium sulfate. The amount of lime added in the reaction with the cesium sulfate containing solution can be any amount and preferably is an amount sufficient to raise the pH of the overall solution to a pH of about 12.5 to about 13.5, and preferably to as high a pH as possible. Adding calcium oxide straight into the cesium sulfate solution can be done for purposes of the present invention. The preferred source is either a slaked lime slurry before addition to the cesium sulfate, or addition of dry hydrated lime.
Generally, with a solution containing cesium sulfate and the maximum addition of lime required to fully react with the cesium sulfate containing solution, from about 8% to about 25% by weight of the originally contained cesium sulfate can be converted to cesium hydroxide. These values are based on the originally contained cesium sulfate in solution after removal of the residue containing the calcium sulfate. The residue may also contain strontium, magnesium, calcium, barium, and/or metallic impurities or other impurities. The residue can be removed by any standard technique for removing precipitates including, but not limited to, filtration and the like.
Once the residue is removed, the remaining solution contains the converted cesium hydroxide as well as any remaining soluble cesium sulfate in solution. There typically is cesium sulfate remaining in the solution since from about 8% to about 25% of the originally contained cesium sulfate by weight is converted to cesium hydroxide after each run. Once the residue is removed, the cesium hydroxide in the solution can then be converted to at least one type of cesium salt. The preferred manner of converting the cesium hydroxide is with the use of an appropriate acid. For instance, if the desired cesium salt is cesium formate, formic acid is used to neutralize the cesium hydroxide that has been generated and that is present in solution. The formic acid causes the formation of soluble cesium formate. Other cesium salts that can be formed by the process of the present invention include, but are not limited to, cesium acetate, cesium citrate, cesium chloride, cesium bromide, cesium nitrate, cesium iodide, cesium propionate, cesium oxalate, cesium butyrates, cesium salicylate, or improved purity cesium sulfate. The appropriate acid is used to form each of these cesium salts, such as acetic acid for cesium acetate. Other acids include citric, hydrochloric, hydrobromic, hydroiodic, nitric, butyric, propionic, oxalic and salicylic.
As indicated earlier, the above-described process can be repeated any number of times until the cesium sulfate in solution is nearly exhausted or totally exhausted. Accordingly, after the first run as described above, the cesium hydroxide has been converted to a cesium salt and thus the solution contains the soluble cesium salt and the remaining cesium sulfate in solution. This solution is preferably then combined with additional lime to form a solution containing at least cesium hydroxide, the previously formed cesium salt, and any remaining soluble cesium sulfate along with the formation of additional residue containing calcium sulfate. The residue is then removed in the same manner as described previously. The cesium hydroxide then is converted to a cesium salt, which can be the same or different from the first cesium salt formed. Preferably, the same cesium salt is formed through the repetition of the process steps described earlier. This process can be repeated as many times and preferably until the cesium sulfate is exhausted or nearly exhausted. The acid and/or lime used after each sequence of repeated steps can be the same or different.
In one embodiment, preferably not all of the cesium hydroxide is converted to or is not immediately converted to a cesium salt since the cesium hydroxide maintains the overall solution containing the cesium salt at a higher pH which enhances the removal of many impurities including, but not limited to, the divalent cations of calcium, barium, magnesium, strontium and metallic impurities like iron, nickel, chromium, manganese, and silicon. The lime has the capability to precipitate metallic impurities out of the cesium sulfate solution. The metallic impurities cited above are commonly precipitated by the elevation of pH. Additionally, while pH alone may not always precipitate the divalent cations, the elevation in pH, consistent with those achieved by this process, is sufficiently high that when followed by the introduction of at least one soluble carbonate source, like carbon dioxide, the divalent cations preferably precipitate as insoluble carbonates and/or other impurities. Other examples of a soluble carbonate source include, but are not limited to, carbonates and/or bicarbonates of cesium, rubidium, potassium, sodium, and lithium or combinations thereof.
With respect to the acid used to preferably convert the cesium hydroxide to the desired cesium salt, the amount of acid added is sufficient to convert up to all of the cesium hydroxide to the desired cesium salt. Preferably, up to, and no more than, a stoichiometric amount of acid needed to convert the cesium hydroxide to the desired cesium salt is added. Generally, when the cesium hydroxide has been fully converted to the cesium salt, the solution containing the soluble cesium salt and any remaining cesium sulfate in solution has a pH typically of from about 7 to about 9; in other words, the solution is substantially neutralized.
The present invention can be further described by the following preferred reaction scheme which is just one example:
STEP 1: First lime addition to neutral 5% cesium sulfate solution.
Reaction 1: Cs2SO4+Ca(OH)2xe2x86x922CsOH+CaSO4↓(8-25% conversion of originally contained Cs2SO4xe2x86x92CsOH)
Reaction 2: MgSO4+Ca(OH)2xe2x86x92Mg(OH)2↓+CaSO4↓.
STEP 2: Filtration of precipitated CaSO4 and Mg(OH)2 solids from CaSO4 saturated cesium liquor.
STEP 3: Neutralization of CsOH contained in the clear filtrate with a desired acid like formic acid.
Reaction: CsOH+HCOOHxe2x86x92CsCOOH+H2O No Precipitate.
STEP 4: Repeat step 1 with 2nd lime addition to neutralized filtrate containing cesium sulfate and formate
Reaction: Cs2SO4+Ca(OH)2xe2x86x922CsOH+CaSO4↓ (Another 8-25% conversion of originally contained Cs2SO4xe2x86x92CsOH)
STEP 5: Filtration to separate precipitated CaSO4 solids from CaSO4 saturated cesium liquor.
STEP 6: Neutralization of CsOH contained in the clear filtrate with a desired acid like formic acid.
Reaction: CsOH+HCOOHxe2x86x92CsCOOH+H2O No Precipitate.
STEP 7: Repeat step 1 with 3rd lime addition to neutralized filtrate containing cesium sulfate and formate.
Reaction: Cs2SO4+Ca(OH)2xe2x86x922CsOH+CaSO4↓ (Another 8-25% conversion of originally contained Cs2SO4xe2x86x92CsOH)
STEP 8: Filtration to separate precipitated CaSO4 solids from CaSO4 saturated cesium liquor.
STEP 10: Neutralization of CsOH contained in the clear filtrate with a desired acid like formic acid.
Reaction: CsOH+HCOOHxe2x86x92CsCOOH+H2O No Precipitate
Step 11: Repeat steps 7 through 10 until all cesium is converted from sulfate to formate, or until desired.
As indicated earlier, preferably substantially no, and more preferably no soluble calcium hydroxide is present in the calcium sulfate saturated filtrate and preferably the lime has fully converted its maximum amount of cesium sulfate to the cesium hydroxide.
The recovered cesium salt can be used for a variety of uses such as, but not limited to, oil field fluids, catalysts, organic synthesis, specialty glass manufacturing, medical uses and for many other applications known to those skilled in the art.
The present invention, in addition, relates to a method of making cesium hydroxide which can then be subsequently converted to other desirable cesium containing products, wherein the method involves reacting a cesium sulfate containing solution with lime as described above to form a solution containing at least the cesium hydroxide and also to form a residue comprising calcium sulfate. As described above, the residue comprising calcium sulfate can be removed and a solution containing soluble cesium hydroxide is recovered along with any remaining cesium sulfate in solution. The cesium hydroxide can then be converted to any desirable cesium containing product, including cesium sulfate, for instance, by adding the desired acid. This method can also be used, for instance, to purify cesium sulfate solution. The action of elevating the pH by adding lime, producing cesium hydroxide and a residue comprising at least calcium sulfate, and separating the residue from the solution, purifies the solution. A soluble carbonate source can be optionally added when the pH is elevated to further purify the solution, precipitating more impurities. The cesium hydroxide can then be neutralized with sulfuric acid to form a higher purity cesium sulfate solution.
The present invention can also be used with other alkali metals (e.g., lithium, sodium, potassium, rubidium, francium). Thus, the above steps can be modified such that any alkali metal sulfate containing solution is used with lime and then using the above-described steps to form any desired alkali metal containing product (e.g., an alkali metal hydroxide, an alkali metal salt, and/or purified alkali metal sulfates).
The present invention will be further clarified by the following examples, which are intended to be purely exemplary of the present invention.